1. Field of Invention
The invention generally relates Class-D audio amplifiers.
2. Related Art
In general, Class-D amplifiers achieve high efficiency and dynamic range. However, they are susceptible to artifact noise, such as pop and click noise, which occurs during amplifier power up and power down. This artifact noise occurs due to the sudden application (during power up) of amplifier DC offset voltage and pulse-width modulation (PWM) pulses to terminals of a speaker to which the amplifier is connected. Similarly, this artifact noise occurs due to the sudden removing (during power down) of amplifier DC offset voltage and the PWM pulses from the speaker terminals. The sudden application and/or removal of the amplifier DC offset voltage and the PWM pulses to the terminals of the speaker generates a transient pulse that discharges through the speaker which causes an undesirable clicking or a pop sound.
Class-D amplifiers are increasingly needed to efficiently drive speakers in mobile communication devices. However in a mobile environment, the amplifier powers up and powers down often. The accompanying pop and click noise therefore limits full adoption of class-D amplifiers in mobile devices. What is needed is a way to suppress pop and click noise in a Class-D amplifier while still preserving its otherwise advantageous characteristics, such as high efficiency and dynamic range.
Features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements.